1. Technical Field
The present invention relates to a substrate for a thin-film magnetic head utilized for a magnetic head slider of a hard disk drive device.
2. Description of the Related Art
Recently, the information content of multimedia data is increasing more and more in association with the requirements of higher definition for video and the like. In addition, it is required for the capacity of an information recording device for recording such video to increase. Hard disk drive devices are information recording devices used as data storing devices of personal computers, recording devices connected to television sets, and the like. For such a hard disk drive device, it is required to increase the capacity thereof and to minimize the size thereof.
FIG. 1A schematically shows a thin-film magnetic slider assembly 10 and a disk (a platter) 13 as a magnetic recording medium included in a general hard disk drive device (hereinafter, sometimes referred to as an HDD). As shown in FIG. 1A, a slider 10A held by a gimbal 14 includes a base portion 11 and a reading element and a writing element 12 (hereinafter sometimes simply referred to as a transducer 12) provided on one end portion of the base portion 11. A unit held by the gimbal 14 is referred to as a head slider, or sometimes simply referred to as a slider.
The writing element of the transducer 12 is formed from a magnetic material. A coil is wound on the inside of a ring, and a magnetic field is generated in the writing element by applying a recording signal to the coil. In this way, data is written onto a disk 13. On the other hand, the reading element as a reproducing head is a magneto-resistive (MR or GMR) effect element, a tunneling magneto-resistive (TMR) effect element, or the like for converting the variation in magnetic field into the variation of electric resistance. The reading element reads magnetic data recorded on the disk 13, and converts the data into electric signals.
The substrate 11 for holding the transducer 12 was often formed by an Al2O3—TiC-based ceramic sintered body. This is because Al2O3—TiC (hereinafter abbreviated to AlTiC) is superior and well-balanced in respect of the thermal property, the mechanical property, and the workability.
In order to increase the storage capacity of HDD, it is required to increase the recording density of the disk 13. Currently, the recording density of HDD reaches about 750 Gbit/square inch. In order to accurately realize the writing/reading operation in such a situation of high recording density, the gap between the transducer 12 and the disk 13 during the operation is preferably small. At present, the gap is as small as 10 nm or less.
In association with the smaller size and higher capacity of a hard disk drive device, the floating height of the thin-film magnetic head from the disk is low, and a higher degree of surface roughness is required for the air bearing surface (ABS) 11a of the slider of the thin-film magnetic head. The ABS 11a is a surface of the base portion 11 facing to the disk 13 in the slider. The shape thereof is designed such as that the ABS 11a is caused to stably float by an appropriate distance from a disk surface due to air flow generated by the rotation of the disk 13 (see, FIG. 1B).
In order to realize the desired shape of the ABS, the base portion 11 is required to have a property to be accurately worked at a nano-level. In general, the base portion 11 is first worked to be flat via a lapping step (a grinding step with a lapping apparatus), and then worked to have the shape with which the above-mentioned air flow can be appropriately utilized by using a dry etching method such as ion milling, ion beam etching, or other methods. In the condition after the above-mentioned lapping step, the worked surface of the base portion 11 is preferably an extremely smooth flat plane.
The gap between the disk 13 and the transducer 12 during the operation may be varied by a factor other than the smoothness of the base portion 11. Hereinafter such a factor will be exemplarily described.
As shown in FIG. 2A and FIG. 2B, the thin-film magnetic head (the slider) 20 is formed by laminating, for example, an AlTiC substrate (the base portion) 21, an Al2O3 film 22, a transducer 23, and an Al2O3 film 24. The Al2O3 films 22 and 24 are typically amorphous alumina. When a thin-film magnetic head 20 is manufactured, a plane 25 which will be an ABS (corresponding to the cut-out plane obtained by cutting the substrate 21 having a thickness t into rod-like bodies 21′ as shown in the lower right portion of FIG. 2B) is first polished to be flat. The plane 25 which will be the ABS (hereinafter referred to as an ABS forming plane) corresponds to a sectional plane of the lamination including the AlTiC substrate 21, the Al2O3 films 22 and 24, and the transducer 23.
In the ABS forming plane 25, since the AlTiC substrate 21, the Al2O3 films 22 and 24, and the transducer 23 are exposed, the difference in hardness among these elements becomes a problem when the ABS forming plane 25 is polished. The Vickers hardnesses Hv of the Al2O3 phase and the TiC phase of the AlTiC substrate 21 are 2000 or more, respectively. The Vickers hardnesses Hv of the amorphous Al2O3 films 22 and 24, and the transducer 23 (metal) are 700 to 900, and 100 to 300, respectively.
Accordingly, if the ABS forming plane 25 is polished so that the polishing amount of the surface of the AlTiC substrate 21 (especially TiC phase) as the main constituting portion of ABS is optimum, the Al2O3 films 22 and 24, and the transducer 23 having the lower hardnesses than the TiC phase are excessively polished. As a result, in the ABS forming plane 25 which is to be flat, the portion corresponding to the Al2O3 films 22 and 24 is lower than the portion corresponding to the AlTiC substrate 21, and the portion corresponding to the transducer 23 is disadvantageously further lower than the portion.
Generally, the step difference is referred to as a pole tip recession (hereinafter abbreviated to “PTR”). Due to the generation of the PTR, an extra gap is formed between the transducer and the magnetic recording medium. This may prevent the increase in recording density and the increase of capacity of the hard disk drive.
As described above, in order to increase the recoding density of HDD, it is required that the distance between the slider and the disk during the operation is controlled as precisely as possible. For example, WO2008/056710 describes a technique in which the organization of an AlTiC substrate manufactured as a sintered body is appropriately formed, so that the mechanical workability can be improved. When an AlTiC substrate with such superior workability is used, a magnetic head with high shape accuracy can be manufactured. Thus, the floating amount of the magnetic head with respect to the disk can be controlled with high accuracy.
One of planes of a slider base portion formed from an AlTiC substrate is subjected to dry etching such as ion beam etching or RIE (reactive ion etching) so as to have the shape of ABS. In the dry etching step, if there are phases of which the etching rates are different, there may sometimes arise a problem that the surface roughness after the dry etching is drastically deteriorated. For example, even if the etching amounts of the Al2O3 phase and the TiC phase included in the AlTiC substrate can be uniform, in the case where an Al2TiO5 phase (an aluminum titanate phase) is generated as a third phase, the etching amount is not uniform. As a result, the surface roughness after the dry etching is sometimes drastically deteriorated.
In the case where the size of a slider is small, when a current flows through a coil which constitutes the transducer, there arises a problem that the quantity of heat generated per unit volume may increase. In this case, the reading element and the writing element are caused to expand due to heat, so as to protrude toward the magnetic recording medium. As described above, the gap between the transducer and the disk during the operation is set to be only about 10 nm, so that the transducer caused to thermally expand may disadvantageously come into contact with the magnetic recording medium.
Such a problem is called as TPTR (Thermal Pole Tip Recession) and is caused by a difference between the coefficient of thermal expansion of the AlTiC substrate portion and the coefficient of thermal expansion of the metal portion constituting the transducer. As a result, during the operation, the transducer comes closer to the side of the disk than expected. The TPTR may easily occur when the thermal conductivity of the slider substrate is small and it is difficult for the heat to escapes. In the case where the transducer is damaged by the contact with the magnetic recording medium due to the TPTR, there arises a serious trouble that the hard disk drive device does not function.
Even when the transducer does not come into contact with the magnetic recording medium, the gap between the magnetic recording medium and the transducer varies due to the thermal expansion of the transducer. For example, when the transducer expands by several nanometers, the gap between the magnetic recording medium and the transducer varies by 10% or more. Accordingly, the writing characteristics and the reading characteristics are largely changed, and some error occurs in the signal written into the magnetic recording medium or the signal read out from the magnetic recording medium.
The AlTiC substrate constituting the base portion of the slider is made from composite ceramic material including the Al2O3 phase and the TiC phase. For this reason, there arise various problems because of the difference in properties of the two phases. As described above, both of the Al2O3 phase and the TiC phase have very hard characteristics, but in more detail, in the AlTiC substrate, the TiC phase is harder than the Al2O3 phase. Thus, there is a difference in hardness between the two phases. Accordingly, when the AlTiC substrate is subjected to lapping, the Al2O3 phase is more ground than the TiC phase. As a result, a step difference (concave and convex) may be sometimes caused in the surface of the AlTiC substrate after the lapping (hereinafter, sometimes referred to as a lapped surface or a lapping worked surface). When the smoothness of the surface of the AlTiC substrate is degraded, the control of air flow between the head and the disk is unstable. As a result, the designed floating amount of the head cannot be obtained, or the floating amount is disadvantageously unstable.
The smoothness is important in the ABS formed by ion milling, or the like. In order to reduce the variation in surface roughness of the ABS obtained by working the shape of a plane, it is preferred to decrease micropores included in the AlTiC substrate. The technique for decreasing such micropores is described in WO2008/056710.
As described above, for the AlTiC substrate for a thin-film magnetic head, various characteristics are required. Especially, the smoothness of the AlTiC substrate after working is important in HDD with smaller size and larger capacity. In addition, it is required that any malfunction does not occur by the influence of TPTR caused by the heat during the operation.
The present invention has been conducted in view of the above-described problems, and the objective thereof is to provide an AlTiC-based substrate for a thin-film magnetic head, and a magnetic head slider and an HDD which utilize the substrate.